I often find myself twiddling dials to play with values and this generally requires tweaking a few different components. Invariably I want to flick between some known state and some experimental state. This would be made much easier by the addition of a bookmark or snapshot function, basically an in memory save function so you can save the current state to a slot in memory and then add a hotkey to flip between states (accessible from the system graph screen for example so I could say cycle alt+1 alt+2 repeatedly to flip between snapshots).

This one I can't do. The structure of the program doesn't allow "state" to be saved. That would require far too much change.

Let me suggest an alternative. You can easily save session files. You also run multiple instances of WinPCD, so you can import this saved session in a second instance of the program. It's not the optimal solution, but it is an option.